In the 3GPP Radio Access Network (RAN) plenary meeting #70, a new study item entitled “Multi carrier enhancements for UMTS” was approved, RP-152227, Study on Multi-Carrier enhancements for UMTS, Huawei, HiSilicon, China Unicom, RAN #70, Sitges, Spain, 2015. As of today, the Universal Mobile Telecommunications System, UMTS, standard only allows for Dual Band—Dual Carrier High Speed Uplink Packet Access (DB-DC-HSUPA) or DC-HSUPA with 2 ms Transmission Time Interval (TTI) on both carriers. In the new study item it was proposed to extend the capability of multicarrier HSUPA by allowing 10 ms TTI to be configured for one or two carriers.
DC-HSUPA was introduced in Release 9 of 3GPP TS 25.212, RP-090014, Study Item “RANimp-DC_HSUPA”, 2009. During Release 13 DB-DC-HSUPA was introduced to add dual band support. In Release 14, the Study Item Description (SID) in the new study states that “10 ms TTI can be configured for multi-carrier deployments. In this way 10 ms TTI can be configured on one carrier or two carriers when DB-DC-HSUPA/DC-HSUPA is configured to obtain higher data rates.”
Based on the SID, a number of possible configurations were foreseen, from which the following scenarios were identified as the most promising ones:
Scenario 1: 2 ms+10 ms configuration for DB-DC-HSUPA scenario
Scenario 2: 10 ms+10 ms configuration for DB-DC-HSUPA scenario
Scenario 3: 10 ms+10 ms configuration for DC-HSUPA scenario
The scenarios have been subject to evaluations, and their potential gains have been compared to legacy performance accounting for both the fixed 2 ms TTI configuration used for both uplink carriers irrespective of DB-DC-HSUPA or DC-HSUPA, and the single carrier performance suitable when the losses between the Network and mobile unit become large because of distance between these entities.
In relation with the possible TTI configurations that can be used by UMTS, enhanced Uplink (EUL) has had the possibility to switch fast between TTI lengths since Release 12. This enhancement allows fast reconfiguration of the User equipment (UE) via a specific set of High-Speed Shared Control Channel, HS-SCCH, orders. Now that the Multicarrier scenarios in the UMTS may potentially deal with independent TTI configurations per carrier, it becomes relevant to revise this mechanism in order to provide a proper handling in both DC-HSUPA and DB-DC-HSUPA scenarios.